A tyre curing mold is in the form of a hollow cylinder, and comprises two opposite, parallel, flat circular sidewalls defining the base walls of the mold; and a number of lateral sectors arranged successively to form the cylindrical lateral wall of the mold.
To insert a green tyre inside the mold and remove the cured tyre from the mold, the lateral sectors are movable radially to and from an engaged position contacting the sidewalls, and are normally pushed radially towards the sidewalls by a system of inclined surfaces activated by a press. This solution is adopted in that it provides for gripping the lateral sectors against the sidewalls with considerable force corresponding to a pressure of 25-30 bars necessary to counteract the pressure (normally at least 20 bars) generated inside the mold during the curing operation.
One example of a tyre curing mold of the above type is described in Patent Application WO2004009337A1.
Because of inevitable tolerances encountered particularly in tyre manufacturing, a surplus portion of the tyre is sometimes pinched between a sidewall and one or more lateral sectors, thus resulting in the formation, on the sidewall of the tyre, of long, circular, extremely thin flash, which tends to curl and is often tough to remove by adhering firmly to the sidewall of the tyre.
Flash in no way affects tyre performance, but, being unsightly, affects the marketability of the tyre and must therefore be removed by further processing, thus increasing the manufacturing cost of the tyre.
Moreover, flash residue on the sidewalls and lateral sectors of the mold must be removed thoroughly, by comprising very hard, cured (bakelized) rubber, which, with repeated closure of the mold, could eventually result in damage to the mold itself. Needless to say, this mold cleaning operation also increases the manufacturing cost of the tyre.
U.S. Pat. No. 4,740,145A1 describes a tyre curing mold, in which flash is prevented by a number of blowholes, which, by blowing on the green tyre, prevent it from being “pinched” between the sidewalls and lateral sectors. Using blowholes, however, is fairly complex, by requiring a compressed air source and, above all, regular cleaning of the blowholes to prevent clogging by rubber scale. Moreover, at the curing stage, the high pressure inside the curing mold may force the tyre rubber partly inside the blowholes, thus resulting in the formation of unsightly “hair” on the tyre.